Technical Field
The present invention relates to horns of motor vehicles and/or water crafts, in particular to EMC (Electromagnetic Compatibility) in the horns of motor vehicles.
Related Art
At present, 90% of horns of the motor vehicles in the world are electromagnetic horns, which have advantages of being low in manufacturing cost and which have defects of being short in service life and have serious problem in regard of electromagnetic radiation interference. This disadvantage is not serious and neglectable when there were electronic devices on vehicles in the past. Along with the development of times, vehicle-mounted electronic devices are rapidly increased from original radios to the fields of motor control, brake anti-lock, steering engine control, window and door control, air conditioner control, vehicle body control, information system, etc. During the use, the original horn may cause, besides the interference to the radio and television due to electromagnetic interference, abrupt vehicle gear shifting and abrupt ON/OFF of the air conditioner of some vehicle models, even more seriously, the ABS brake system to fail briefly when the horn is pressed, and thus driving safety is greatly affected.
For this purpose, electronic vehicle horns emerged in the 1980's of the last century. Although the electronic horns are greatly improved than electromechanical horns in the aspect of EMC, due to the limitation in cost of the electronic horns and a limited space in the horns per se, the electromagnetic interference generated by an electromagnetic oil of the horn cannot be effectively inhibited; meanwhile, the electronic horn will cause the horn oscillation system abnormal at some frequency points, or even cause oscillation stop to damage the horn when performing high frequency bulk current injection interference test.
In the ON/OFF process of the vehicle-mounted electrical equipment, for example, when the motor or ignition system is on/off, the transient interference phenomenon may be caused by wire bundle distribution capacitance and inductance and, when the horn is tested according to CIRS25, Conducted Emission and Radiated Emission (i.e., the radiated electromagnetic emission harassment test) go severely out of limit at some frequency bands. The horn may be even damaged during BCI interference test and interference pulse injection test in accordance with ISO7637 standard. However, the vehicle manufacturers have no other options. The horn EMC non-compliance has been a difficult problem in the manufacturing industry of the electronic horns.
Since the horn has a metal overally-enclosed shell, the shell of the horn is grounded no matter in test or in use on the vehicles, and about 95% of the conducted emission and radiated emission are leaked from a power supply terminal of the horn. In the EMC test of the existing horns, the conducted emission and radiated emission go seriously out of limit according to the international standard CIRS25 (FIG. 3). Thus, the manufacturers of the electronic horns tried a variety of ways to absorb or inhibit the high frequency electromagnetic interference generated during working of the horn. There are some common methods as follows:
First method: capacitors are used at two ends of driving electromagnet coils, i.e., the main interference generating source, of the horn for absorbing, the defect is that an audio pulse string of driving horn electromagnets is enabled to pass by a bypass of the capacitors when the capacitance of the capacitors is increased to some extent, such that the horn driving current is increased while electromagnet driving power is reduced, the interference inhibition action is not effectively improved, the sound of the horn is reduced, and the first method cannot be used.
Second method: serial capacitors and resistors are adopted at two ends of the of driving electromagnet coils, i.e., the main interference generating source, of the horn for absorbing. The portion of current, bypassed by the capacitor and resistor bypass, of the audio pulse string of the driving electromagnet coils, is reduced and thus the horn driving current is reduced, but the interference inhibition action is not effectively improved, and thus the second method cannot be used.
Third method: transient diodes or fast recovery diodes are mounted at two ends of the driving electromagnet coils of the horn for absorbing. But due to the follow current influence of a diode switch, the horn driving current is increased, but the electromagnet driving power is reduced, the horn power consumption is out of limit, the sound is reduced, and thus the third method cannot be used. Although the driving current increment is reduced to some extent by serially connecting the resistor to the diode, the interference inhibition action is not effectively improved, and the third method cannot be used.
Fourth method, since the working current of the horn is 2-6 A, a conventional method is to add an inductor and a high frequency capacitor (less than 1 microfarad) and a magnet ring at a power source input terminal to filter, but due to a large volume, they cannot be mounted in the horn, the interference inhibition action is not effectively inhibited either, and thus the fourth method cannot be used.
The methods of all forms similar to the above methods are used to absorb the counter emf of the coil, in the final analysis, the problem of CIRS25 interference disqualification is solved by using an absorbing inhibition method, but due to the poor effect, the EMC index of the horn does not conform with the CIRS25 standard always.